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EPDM Synthetic Rubber is not Fully Compatible with Swimming Pool Chemistry
Almost every solar pool heating dealer that has any lengthy experience has run into the phenomenon of black goo, dust or particles oozing out of an EPDM synthetic rubber solar collector, making a mess of the pool. Many times the customers aren't too upset because they got 6 or 8 years service out of their solar heater and this has been good service. Some have even lasted 20 years or more. Besides, the systems have usually paid for themselves many times over. No harm no foul. We at Hot Sun have studied this issue carefully because we believe that first and foremost solar pool heaters need to be flexible so they can be repaired, serviced, and so they can tolerate frost conditions (42F exposed to a clear night sky). Keep that in mind when someone selling rigid polypropylene solar panels tells you about black pool. They have a bias and so do I. EPDM is tough and it doesn't necessarily have to be glued to the manifold. Rubber stretches elactically whereas plastics can deform plastically. Look up the meaning of the word plastic. At Hot Sun we have always used thermo plastic based materials with zero risk of this kind of breakdown but during our technology development we did stray toward EPDM momentarily for its obvious appeal and we were punished.
The rumors and stories on the epdm breakdown topic have circulated by word of mouth since long before the internet age. Dory Mowlavi (now retired) , owner of Solartrope Supply Corp, in Orange CA announced to us in 1989 that the epdm rubber tubing breaks down sometimes so his suppliers had switched materials to "Santoprene". A year later the story was that Santoprene broke down even quicker. Oops. The video below from San Diego was taken by Hot Sun when we were called out to witness this in an 8 year old system that had been shut off for a month or so. The owner knew that when he moved the water thru solar the black crud that had developed would come off and we needed to document it. Note it doesn't happen continuously, only when solar is first turned on after being off a while and this is a particulary bad epdm product. Its softer and has a larger diameter cross section than most so its breakdown characteristic we believe is more severe than some. We know many solar owners who simply filter or flush this crud out when they start their system each spring. We believe this happens with all EPDM collectors but please note that with small diameter stiffer products the effect is much less pronounced and it presents in differet ways. Particles are easier to deal with than clouds of fine dust like this.
Solaroll was the biggest and most prolific product of this kind. It has now resurfaced in South Africa and claims a long history (since 1977) in the business.
Tom Lane is a famous solar pool heating contractor in Central Florida. His recently published book, "Solar Hot Water Systems Lessons learned 1977 to Today" chronicles his experience in this industry. He flat out states on page 183. "WARNING: DO NOT BUY RUBBER MAT POOL COLLECTORS (EPDM RUBBER) THEY CANNOT STAND UP TO POOL CHEMICALS"
Hopefully Tom Lane won't mind me quoting that line from his book if I provide a link here to his web site where you can buy it yourself. Its an awesome chronicle of his life's experience with this technology.
This set of photos shows the Franklin Health and Fitness Center's epdm system that we supplied and the breakdown of the solar collector. We have an affidavit on file from the owner of the Health club as well as from the contractor who installed the replacement system and we kept some of the collectors just in case anyone wants to challenge us on these facts.
Usually water has to sit in the collector for a while and heat up before the reaction re-occurs. At Franklin, we didn't experience any of those things. It just started oozing black particles and only in year 3 and the epdm was from a solar manufacturer that had been using the same formula for 27 years. The point is we can't predict which situations will suffer epdm breakdown so we developed a flexible collector that simply won't break down and that is our fundamental technological achievement and we're very proud of it. It allows us to not have to worry about it and it allows us to guarantee against it and that is woth the extra effort and risk of having to glue the fin tubes to the manifolds. Turns out the adhesive lubricates and makes that assembly actually easier once you have a little experience. The downsides to plastic turned out to not be significant.
More evidence of a sort. This was a worldwide problem. EPDM was the standard solar pool heating material 40 years ago. In Australia this problem occurred as well. The solution there was to switch to a plastic based alternative like we had. For years Hot Sun aligned ourselves with various Aussie competitors in this.
There are many papers on the subject. We believe based on what we have been able to gather is that the effect is caused by the chloramines. These are the combined chlorines created when free chlorine disinfects organic matter. You can't avoid this if you're using chlorine to sanitize the water. Heat is a big factor in breakdown as well. You can't avoid the heat of a black thing in the sun with the pool up to temperature. We protect you against the possibility of this phenomenon for 25 years as you see in the Powerstrip warranty.
As a footnote, we've sold two other large commercial solar pool heating systems in North Carolina since we replaced the one above using it as a reference. It always pays to behave with integrity even if your only objective is to make money
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